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Effects of humidity on the electronic properties of graphene prepared by chemical vapour deposition

We correlate the local and global electronic properties of mono- and bi-layer chemical vapour deposition (CVD) graphene transferred on SiO2 by simultaneously performing local surface potential (and calibrated work function) measurements using Kelvin probe force microscopy and global transport measurements in the van der Pauw geometry in an attempt to investigate the effects of humidity on the electronic properties of CVD graphene.

Using controlled environmental conditions in a scanning probe microscope chamber, we investigate the effects of humidity on the electronic properties (work function and carrier concentration) of CVD graphene of different thicknesses. We show that presence of water vapour leads to p-doping of both mono- and bi-layer graphene, with saturation occurring at ~40% RH. However, the response of humidity on artificially (double transfer of individual mono-layers) bi-layer graphene is similar to mono-layer, which is in contrast with the response of the as-grown 2LG islands. Furthermore, we demonstrate that the general belief that water vapour present in ambient air is responsible for the high hole concentration observed in CVD graphene is inaccurate, as both work function and hole concentration did not reached the initial ambient levels even at 60% RH, thus other gases are also responsible for the doping in ambient.

This work indicates that electronic devices using CVD graphene on SiO2 must be properly encapsulated to ensure stable operation, and sensors must be appropriately calibrated to minimise the effect of ambient humidity.